1. Field of the Invention
The present invention relates to a switch circuit, and more particularly, a radio frequency switch circuit formed by MOS transistors or junction field effect transistors using silicon.
2. Description of the Related Art
As switch circuits for radio frequency such as a single pole dual throw (SPDT) switch circuit or a double pole dual throw (DPDT) switch circuit, GaAs field effect transistors (FETS) have been used (see: Robert H. Carevly, "Distortion in GaAS MESFET Switch Circuits", Microwave Journal, pp. 106-114, September (1994)).
The switch circuit using GaAs FETs is very simple and therefore, can be constructed by one semiconductor chip. Also, since the mutual conductance g.sub.m and the transition frequency f.sub.t of GaAs FETs are very high, the characteristics of the switch circuits can be enhanced. This will be explained later in detail.
On the other hand, the gate length of MOS transistors or junction FETs using silicon has become fine. For example, such a gate length is less than 1 .mu.m. Therefore, the mutual conductance g.sub.m and the transition frequency f.sub.t of MOS transistors or junction FETs using silicon are also very high. Since silicon is less expensive than GaAs, and switch circuits using silicon can be easily integrated into other integrated circuits, switch circuits using silicon are preferable.
However, if the GaAs FETs of the above-mentioned radio frequency switch circuit are simply replaced by MOS transistors or junction FETs using silicon, the transmission loss of radio frequency signals is remarkably increased which will be explained later in detail.